Failed to call service light/turn_on with unsupported operad type(s)

Learning Home assistant, in pursuit to create my own MQTT controlled light, with json schema, to minimize number of messages.

My test auto discovery message looks like:

    "~": "ha/tm/8R-1L-1TS-123498DB/rgbstrip/04",
    "name": "RGB strip 04",
    "object_id": "rgbstrip_04",
    "unique_id": "rgbstrip_123498DB_04",
    "device_class": "light",
    "schema": "json",
    "cmd_t": "~/c/cmd",
    "stat_t": "~/s/stat",
    "optimistic": true, /* set to true for test purposes only */
    "on_command_type": "first",
    "brightness": true,
    "white": true,
    "supported_color_modes": [
    "effect": true,
    "effect_list": [
    "device": {
        "identifiers": [

Which properly generates new entity and displays controls:

They all work properly, except when I click to W to set white color, then I get:


When I select RGB color, I properly get MQTT message similar to:

  "state": "ON",
  "color": {
    "r": 81,
    "g": 159,
    "b": 255

What am I doing wrong that white doesn’t work?

Found the issue. It is necessary to first set some brightness with the frontend slider, only then pressing “white” button will properly transmit message to the light.